Telephone system.



K. S. JOHNSON.

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KENNETH S. JOHNSON, OF JERSEY CITY, JERSEY, ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

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specification of Letters Patent. 'd ,application med septenber 25,1917. semina. 193,104.

"m new .and useful Improvements in'Telephone TELEPHONE sYs'rEin.

Y cord circuitssilnilarto C, but'for convenience onlythe two lines and the onev cord 'circuit have been shown.'

. Patented. cees, 1918.

An operators telephone set D, common to a plurality of 'cordcircuits C, comprises an lnductionfcoil having 'a primary 21, in

Y' avea v telephone circuits -for use in telephone lsystions to connect the telephone set across the thetransfmission eiiiciency-oflth'e circuit be- .20

'v decreased by'-v such connection.of'the'operators telephone' set. f

mis.

line,'is highlgy eiiicientfor-both talking-.and receivin,A and monitor Yng purposesl will notl materially de-.

. erators telephone circuit isv provided 'with .,Systems, of which the .following is a full, clear, concise, and exact description'. pedancecoil23 and a condenser 24." A trans'- y Thisv invention relatesk to Atelephone sys- Init-ter 25 .connected as shown, so as to tems, and more particularly to operators]A receive battery. supply from battery 22 through an impedance coil-23, and to be in tems. s -V Vthe talking circuit which includes y the pri- When establishing connections between mary 21 of the inductioncoil andthe con-- toll and local telephone lines, it is necessary denser 24. Upon the same core with the prior an operator'in supervising suchconnec-v maryv 'winding 21 is wound a secondary y l winding comprising-four sections/26, 27, 28 vcircuitestablished betweentwosubscribers@1and29, all of which are connected in series Undesuch circumstances it is essential that` aiding.' The impedance of section 27 is 'of thesame value as that of section 28, while tweenthe two `subscribers bent materially -the impedance of sections 26 and 27 in series isof the same value as that of sections 28 lAn objectpf this invention therefore,jf26 and 29 is low compared to that of secs circuit with Vwhich is a-battery 22,' an imand 29' inseries. The'resistance of sectionsv the productibn' ofi an operatoris telephone circuit which; when connected to a telephone tions 27 and 28, receiver 30 has one ter-l minal connected tothe junctionpoint vbetween sections 26 and 27, and theV other teri -ininal thereof normally connected through the normal right-hand contactof relay 40 to the junction point between sectionsl .28 and 29,- With thereceiver connected in this which whenfbridged across fthe talk g circuit between'subscribers for.

' 'crease the transmissionefliciency of the talk l f In accordan'ce-with this'jinventionan op-i y:duction coil 20 acts as an auto-transformer dle point of the secondary winding at the junction point between sections 27 and l28 is grounded to balance both sidesof the operators, telephone circuit, thereby to eliminate inductive noises in the receiver from ringing` current traversing adjacent leads in van induction coilhavin'g'a secondary winding vwith va recelver normallyv connected Upon the actuation of a key or switch asso- .v ciated with an operators link Vcircuit connectingtwotelephone lines together, the receiver is connected in bridge of a low imsections 29 and 26 of the secondary winding -pedance 'section ofthe secondary winding and thereby increases the impedance of the bridge including the secondary winding,

which as a result of the actuation of the switch -is connected across the talking cir.-

cuit extending between the two subscribers-- This invention is illustrated in the accoml panying drawing in which there is shown a the-switchboard. The louter terminals of are connected to conductors 31 and 33 respectively terminating in normally open contacts of a listening key9 and norm-ally `open contactsof a slow-tofoper'ate relay 41 manner, the secondary winding ofthe infor 'receiving incoming currents. The f.mid

ico

erators telephone circuit as clearly set forth in U. S. Patent No. 1,232,884, issued to scar E. Benson, July 10, 1917. The junction point between sections 27 and 28 ot' the secondary winding and the junction point between resistance coils and36 are normally grounded through the left-handy normal con tact of relay 40.

If the operator desires to converse with either subscriber, listening key 9 is actuated to connect the tip and ring conductors 33 and 3l of the telephone set with the talking strands of the cord circuit, thereby bridgin the telephone set acrossthe circuit. .Shoul the operator merely'desire to bridge'the receiver of the telephone set across the circuit established between A and B for the purpose of properly supervising the connection between the subscribers or for any other purpose, a monitoring key 10 is actuated. Upon the actuation of this keycontact 11 thereof is closed to cause the energization of relay 40, which thereupon .causes the following operation to take, place: (1) opens contact 42, thereby-openingup the primary circuit including the induction coil primaryl 21 and the transmitter 25 to prevent outside noises from being induced into the secondary winding; (2) opens contact 43 thereby removin the ground from the middle point vof t e secondary winding and p the junction point .of the two resistances 35 and 36 to prevent the possibility' of noises on the line due to such ground; (3) opens contact 44, thereby disconnecting the receiver 30 from bridged relation with sections p 27 and 2S; (4) closes contact 45, thereby connecting the lreceiver 30- in bridge ,of the low impedance section 26; and (5) closes contact 46 causing the operation of the slow-to-operate relay 41 which then coperates with the monitoring key l0 to connect the tip and ring conductors 33' and 31 of the telephone setV with the talking strands of the cord circuit. The secondary winding increased, thereby having less effect upon* the transmission efficiency of the circuit between subscribers A and B.

It is'to be observed that this invention provides an operators telephone circuit iny which a single induction coil may heemployed for ordinary Italking and receiving,

and which may be then connected in bridger of a telephone line for monitoring purposes, and when soconnected the effective impedv responsive to the actuation ot 1s now bridged across the talking strands of ance of the bridge is materially increased to produce as little shunting eifect for talking` currents as possible.

What is claimed is:

1. In a telephone system, in combination, a telephone line, an induction coil having a primary and a secondary winding, a transmitter and a source of current in circuit with the primary winding, a receiver in op? erative relation to the secondaryv winding, a switch, a bridge including the secondary winding connected across the telephone line upon the actuation of the switch, a second switch controlling the connection of the bridge across the-telephone line, and means effective upon the' actuation of the second switch for altering the impedance of the bridge.

2'. In a telephone system, in combination,

a telephone line, an induction coil having for increasing the impedance of the `bridge i 'before the connection thereof to the telephone line. n 3. In 'a telephone system, in combination, atelephone lin'e, an induction coil having a primary and a secondary winding, a transmitter and la source of current in circuit `with theprimary winding, a receiver in operative relation to the secondary winding, a

switch, a bridge including the secondary winding' connected across the telephone line upon the actuation .of the switch, a secondswitch controllingthe connection of the bridge across the telephone line and a relay the second switch for increasing the impedance of the bridge before the connection thereof to the vtelephone line.

. 4. In a telephone'l system, in lcombination,

a telephone line, an induction coil having a primary and a secondary winding, a transmitter and a source of current in circuit with the primary winding, a receiver in operative relation to the. secondary winding, a switch, a bridge including the secondary winding connected across the ltelephone line upon the actuation of the switch, a second switch, a relay responsive to the actuation of the second switch for altering the impedrancev of the bridge, and a second relay con-, tiolled by the second switch for connecting the altered bridge to the telephone line.

5. In a telephone system, in combination. a telephone/line, an induction coil having a primary and a secondary winding, a transwinding connected across the telephoneline upon the actuationy of the switch,` a. second switch, a relay responsive to the actuation of the second rswitch for increasing the impedance of the bridge, and a slow-to-operate relay operatingiipon the response of the first relay for-thereafter connecting the bridge to the telephone'line.

k6. In a telephone system, in combination, a telephone line, an induction coil having a primary and a secondary winding, a transmitter and a source of current in circuit with the primary winding, a receiver normally connected in bridge of a portion of the secondary winding, a switch when actu.

ated causing the connection of the secondary winding to the telephone line, and means effective upon the actuation of the switch for connecting the receiver in bridge of another portion of the secondary winding.

7. In atelephone systerrnin combination, a telephone line, an induction coil having a Vprimary and a secondary winding, a transmitter and a source of current in circuit with the primary winding,ia receiver normally connected in bridge of a portion of the secondary winding, a switch when actu/- ated causing the connection of the seconda winding to the telephone line, and a relay responsive to the actuation of the switch for connecti g the receiver in bridge of another portion of the secondary winding.

8. In a telephone systeinl, in combination,

a telephone line, an induction coil having a primary .and a secondary winding, a transmitter a d a source of current in circuit with thellprimary winding, a receiver lnormally connected in bridge of a portion of the secondary winding, a switch, a relayjresponsive to the actuation of the switch ffor connecting the receiver inbridge of another portion of the secondary winding, and another relay controlled by the switch for thereafter connecting the secondary winding .to the telephone line. ,i

9. In a telephone system, lin combination,

. a telephone line, an inductibn coil having a primary and a'secondary winding, ai transmitter and a source of current in circuit with the primary winding, a receiver nor mally connected in bridge of a portion of the secondary winding, a switch, a relay energized upon the actuation of the switch for connecting the receiver in bridge of another portion 'of the secondary winding, and a slow-tooperate relay operating upon the energization of the first relay for thereafter connecting the secondary winding to the telephone line.

10. In a telephone system, in combination, a telephone line, an induction coil having a primary winding, a transmitter andl a source of current in ycircuit with the primary'winding, asecondary winding-for theinduclionl.

coil grounded at its middle point, Va receiver normallyy connected inbridge of'af'portiou of the secondary winding and in symmetrical relation to the'ground thereof, a switch when actuated causing' the connection of the seconary winding to the telephone line, anda relay responsive to the actuation ofV the switch for removing the ground from" the secondary winding-:and connecting 'the receiver in bridge of another portion thereof.

115 In a telephone system, in combination, a telephone line, an induction coil having a primary winding, a transmitter and a source of current in'circuit with the primary wind ing, a secondary winding kfor the induction coil grounded at its middle point, a receiver normally connected in bridge of a portion e of the secondaryi winding and in symmetrical relation to the ground thereof, a switch, a relay responsive tothe actuation of the switch for removing the ground from thesecondary winding and connecting the re: ceiver invfbridge of another portion thereof, andanother relay operating under control of the switch for thereafter lconnecting the secondary winding to the telephone line.

l2. In a telephone system; in combination`l a telephonejline, an induction coil having a primary winding, aitransmitter and a source of current in circuit with the primary winding, a secondary windingrv for the induction coil grounded-'at itsLmiddle point and comprising sections of high and'low resistance, fareceiver normally connectedin bridge of a high resistance section of the secondary kwinding and in symmetrical relation to the 'ground thereof` a switch when actuated causm l= ing the connectionV of the secondary winding tothe telephone line, and a relay responsive to' the actuation of the switch for'removing the ground from thesecondary rwinding and connecting the receiver in. bridge .of a low resistance section thereof.

18. In a telephone system, in combination, a telephone line, an induction coilhaving a primary winding, a transmitter and a source of current in circuit with the primary windin' a secondary windingfor the induction coilgrounded at its middle point and comprising sections of high and low resistance,

a` receiver normally'connected in bridge cfa high resistance section of. the secondary winding and in symmetrical relation to thev ground thereof`r a switch, a relay responsive to the actuation of the switch for removing the ground from the secondary winding and connecting the receiver in bridge lof a low resistance section thereof, and a slow-topperate relay operating under control of the switch and cooperating therewith for thereafter connecting the secondary winding to the telephone line.

14. In a telephone system in combination, a telephone line, an induction coil havlng a primary Windlng, a transmltter and a source of current in circuit with the primary Wind ing, a secondary Winding for the induction coil comprising two sections of high and two of low resistance and having its middle point grounded, a receiver normally connected in bridge of the high resistance sections and in symmetrical relation to the ground of the secondary Winding, a switch, n relayenergized upon the actuation of the switch for KENNETHS. JOHNSON. 

